Digital-to-analog (D/A) and analog-to-digital (A/D) converters are used generally in electronics, especially in computer interfaces, to convert an analog signal into digital form, and vice versa. In rapid and accurate converters, it is customary to use a binary weight system in which the base number is 2: EQU U=(C+B.sub.1 2.sup.-1 +B.sub.2 2.sup.-2 + . . . +B.sub.n 2.sup.+n)E, (1)
where U is the value of an analog signal, E is a reference voltage used in the converter, and B.sub.1 . . . B.sub.n are binary values (0,1) C is a constant and n is the number of the bits/weights of the converter.
The binary weights 2.sup.-k of the converters are usually realized by weight or reference elements forming a so-called weighing network. In practice, the weighing network and the weight elements are usually realized by means of resistors, capacitors and transistors. The accuracy of the converter thereby depends on how accurately the relationship between the values of the weight elements is the right one. This involves very high requirements for the converter manufacturing technique, and in many cases converters have to be tuned after manufacture. Further, as the values of the weight elements vary in time (drifting), the accuracy limit of converters is usually about 12 bits. Converters having a greater accuracy than that have to be calibrated or tuned intermittently during use.
Converters usually have to be calibrated by adjusting the values of the weight elements and the reference voltages.
In addition, when great speed and accuracy are to be achieved, the time required for the converter to settle to the required accuracy causes problems. For this reason, the most accurate conventional converters are usually also slow.